398 



MR. E. A. SMITH ON SHELLS FROM ADEN. [JuUC 16, 



Tlie following table also lends some support to this proposition. 

 It will be noticed that, starting from Australia ^ and the Philippine 

 Islands, all are found in the Red Sea, four at the Cape, one has been 

 recorded from St Helena, one from Ascension, six from the Atlantic 

 Islands, and all in the Mediterranean. 



Name of species. 



cs.2 



? ^ 



Chiton sicuhis 



,, discrepans .... 



Philine aperta 



Lima inflata 



Area lactea 



rfinerupis irus 



Petricola Uthophaga . 

 Gastrochcena dvbia . 



It is quite possible that most of these species may have been 

 carried across the Indian Ocean ^ to the Cape in various states of 

 development, for we know that a very large quantity of pumice 

 thrown into the sea during the eruption of Krakatoa in 1883 was 

 drifted in that direction, indicating the course likely to be taken by 

 larval and pelagic forms or even by adult organisms (like the last 

 five of the above species) if attached by a byssus to, or burrowing 

 into, floating substances like pumice. Passing the Cape they may 

 have extended up the West-African side of the Atlantic past the 

 Atlantic Islands ^ and so on into the Mediterranean, at the entrance 

 of which at Gibraltar, the main strong surface current is from the 

 Atlantic eastward, which would of course be favourable to the influx 

 of species from that sea. 



As I have before stated, this is all mere conjecture, and we have 

 to assume a starting-point somewhere in the East, for which we have 

 no grounds. The proposition that species common to the Red Sea 

 and the Mediterranean may have originated in the East, holds good 

 also in regard to three of the four species which I consider sufficiently 

 different from the Mediterranean species to be regarded as distinct. 

 Even if we consider them practically identical, as Mr. Cooke does, 



1 Euikria cornea was recorded from New Caledonia by Brazier in 1889, and 

 the 'Challenger' dredged off Sydney about 10 species of Mollusca wliich are 

 inseparable from N. Atlantic forms. 



^ We conjecture that the ocean-currents took the same direction in bygone 

 days: what grounds have we for this? 



^ Vide my reports on the Mollusca of St. Helena and Ascension Island 

 (P. Z. S. 1890, pp. 247, 317). 



